(1) Field of the Invention
The present invention relates to a blood pressure measurement device and methods for measuring blood pressure. More specifically, the present invention relates to apparatus and methods for determining whether a patient was in a rest condition during blood pressure measurement.
(2) Description of Related Art
A rest condition of a patient is important when measuring blood pressure. If the patient is not in a rest condition, the measured blood pressure may differ from the value measured in the rest condition. Thus, it is necessary to know whether the patient was in the rest condition when the blood pressure was being measured.
As a measure to determine whether a patient was in a rest condition, measuring pulse rate and pulse wave period is known. Generally, the patient's pulse wave period becomes short or unstable after hard exercise or mental distress. Therefore, it is possible to determine whether the patient was in the rest condition by examining whether the patient's pulse wave period was stable during a certain period of time.
Rossmax Hemodynamic Stability Determination (HSD) determines a rest condition of a patient by measuring the patient's pulse period. However, because each individual has a significantly different pulse period in connection with both pulse rate and pulse period change, it is difficult to determine whether the patient was in a rest condition or an unrest condition at the time of measurement of blood pressure by comparing the measured pulse period with a general or standard value of the pulse period.
JPH2012-120206 discloses a relationship between the pulse rate and the pulse period change. As shown in FIG. 9 of JPH2012-120206, when a patient receives a stress, the pulse rate and the pulse period change of a patient are influenced differently by the stress. Therefore, it is possible that when the pulse period change of the patient is significantly increased over a certain period of time by receiving a stress, the pulse rate over the same period of time remains unchanged. Therefore, when the pulse period is measured in order to determine the rest/unrest condition of the patient, examining the pulse period change (variability) in addition to the pulse rate is useful and desirous.
In addition, the pulse wave period of a patient is significantly influenced by the time zone (time of day), day of the week, season, environmental temperature, etc. Thus, these conditions at the time of measurement should also be taken into account.
Because prior art blood pressure measurement devices do not adequately consider that the rest or unrest condition significantly differs from patient to patient, these devices may provide inaccurate blood pressure value measurements.